RadMultiColumnComboBox can cascade from another RadMultiColumnComboBox instance.
It takes the value from the DataValueField of the parent instance
set in its CascadeFrom property, and uses it to filter its data source.
If a combo box is cascading, it will be disabled until its parent has a value.
You can control the field that is filtered in the current data source
through the CascadeFromField property, and the field from the parent data source that is used as a filter value
through the CascadeFromParentField property.